Optical beam steering involves redirecting a beam of light to a predetermined direction. More complicated beam steering applications involve redirecting the beam to a continuous one or two dimensional path, i.e., a scan or trace. Such applications include optical processing, laser scanning such as for laser printers, and optical memories.
Many existing beam steering devices operate on some principle of moving a lens or mirror to change the direction of a transmitted or reflected beam. One existing beam steering method involves shifting one layer of transmissive lenses with respect to another layer of lenses. This method is discussed in an article entitled "Agile Beam Steering Using Binary Optics Microlens Array", by W. Goltsos and M. Holz, Optical Engineering, pages, 1392-97, November 1990. Other optical beam steering devices direct the beam with spinning mirrors. A problem with such devices is that they must provide some mechanical means for providing translational or rotational motion to the lens or mirror. Thus, they are limited in speed of operation and susceptible to mechanical failure.
An alternative approach to beam steering is the use of spatial light modulators (SLM's). SLM's are typically configured as one or two dimensional arrays of individually addressable optical elements. A common application of SLM's is in display systems, in which these elements represents pixels of an image and modify either the amplitude or the phase of light distribution within the optical system. SLM's can be divided into various types, including electro-optic, magneto-optic, liquid crystal, and deformable mirror devices. Various types of SLM's are discussed in the background of U.S. Pat. No. 4,956,619, which is incorporated by reference herein.
For beam steering, SLM's receive an input beam and the pixel elements are micro-mechanically moved to redirect the beam. An advantage of using spatial light modulators for beam steering is that no translational or rotational motion of a large external lens or mirror is required. The directionality is provided by reflecting the light from a stationary modulator that changes its phase, position, or shape. Another advantage is that SLM's are easily manufactured in sizes appropriate for the size of light beams used for communications. Advanced techniques for fabricating SLM's, including their addressing circuits, as integrated circuits have been developed.
A problem with using spatial light modulators for beam steering is the small size of the reflective elements. A single reflective element is typically smaller than the beam to be steered; and if an array of reflective elements is used, diffraction is a problem.
A need exists for an improved means for using spatial light modulator concepts for steering a beam of light.